1. Field of the Invention
This invention relates to a system for warming blood and other liquids to physiologic temperature before infusion into a patient. The system is characterized by an external cylindrical heating surface around which is wrapped a flat disposable heat exchanging liquid warming envelope with automatic gas bubble venting and by an internal cylindrical heating surface with radial air warming fins for the provision of active warm air insulation of the intravenous line to the patient.
Blood is stored at approximately 4 degrees C. prior to transfusion and should be warmed to physiologic temperature of about 35 to 40 degrees C. for transfusion. Infusion of cold liquids at high flow rates can cause cardiac arrhythmias, cardiac arrest and death. Even at low flow rates it is desirable to warm intravenous liquids for delivery to the patient, especially if the patient is an infant or child, has cardiac disease or is otherwise of fragile health.
In the intravenous administration of blood products and other intravenous liquids, it is necessary that the liquid being administered to the patient be free of entrained air or other gas bubbles to prevent venous gas embolism and its potentially fatal consequences. The present system is designed to deliver warmed liquids from very low flow rates to high flow rates of 500 ml/min or more. At high flow rates significant volumes of gas bubbles are generated during the warming process. These must be removed before administration of the liquid to the patient.
2. Prior Art
My prior U.S. Pat. No. 5,013,889 is directed to an electric blood warmer utilizing heating by vapor condensation. My prior U.S. Pat. No. 5,420,962 is directed to a convection blood warming system having an automatic hydrophobic vent incorporated in the disposable flattened tube plastic heat exchanging envelope and utilizing active warm air insulation of the intravenous line to the patient. The disclosure of those patents are incorporated herein by reference.
One commercially available blood warmer (Baxter ThermaCyl Blood/Fluid Warmer) employs an external nearly cylindrical (actually conical) heating surface. Another (American Medical Systems DW 1000 blood/fluid warmer) utilizes a cylindrical heating surface. Both include conventional electrical convective heating units and flexible plastic film cuffs through which the blood flows. Neither includes air heating means.
One object of the present invention is to provide the increased constant heating surface temperature characteristic of heating by vapor condensation. Another object of the present invention is to utilize an internal cylindrical heating surface extended by fins for air warming to actively insulate the intravenous line to the patient.